Burkholderia pseudomallei is a saprophytic, gram-negative bacillus widely distributed in tropical soil and water.
Through inhalation or subcutaneous inoculation, occasionally by ingestion; person-to-person transmission is rare via contact with the blood or body fluids of an infected person.
Endemic in Southeast Asia, northern Australia, Papua New Guinea, much of the Indian subcontinent, southern China, Hong Kong, and Taiwan. It is considered highly endemic in northeast Thailand, Malaysia, Singapore, and northern Australia. Melioidosis has been reported in Puerto Rico, suspected in El Salvador, and may be underdiagnosed in India, Africa, the Caribbean, and Central and South America. In northern Brazil, clusters of melioidosis have recently been recognized and are associated with periods of heavy rainfall. The risk is highest for military personnel, adventure travelers, ecotourists, construction and resource extraction workers, and other people whose contact with contaminated soil or water may expose them to the bacteria. Risk factors for systemic melioidosis include diabetes, excessive alcohol use, chronic renal disease, chronic lung disease (such as associated with cystic fibrosis or chronic obstructive pulmonary disease), thalassemia, and malignancy or other non-HIV-related immune suppression.
Incubation period is generally 1–21 days, although it may extend for months or years; with a high inoculum, symptoms can develop in a few hours. Melioidosis may occur as a subclinical infection, localized infection (such as cutaneous), pneumonia, meningoencephalitis, sepsis, or chronic suppurative infection. The latter may mimic tuberculosis, with fever, weight loss, productive cough, and upper lobe infiltrate, with or without cavitation. More than 50% of cases present with pneumonia.